This invention relates to the field of therapeutic, diagnostic, or hydrophilic coatings for intracorporeal medical devices.
The use of a medical device within a patient may be facilitated by the presence of a therapeutic, diagnostic, or hydrophilic agent on the device surface. For example, intravascular devices, such as catheters and guidewires, are more easily maneuvered within a patient""s vasculature when the friction between the walls of the vessel and the intravascular device is reduced. The friction may be reduced by coating the device with a hydrophilic compound which becomes slippery after adsorbing an appreciable amount of water. Consequently, the hydrophilic coating provides lubricity when the coated device is exposed to aqueous solution, as when the coated device is exposed to water prior to insertion in the patient or to the patient""s blood during use. Alternatively, coatings, such as fluoropolymers, and silicone, provide lubricity to the surface of an intracorporeal device without the need for exposure to aqueous solution. However, the degree of lubricity may vary greatly depending on the nature of the lubricious coating. Hydrophilic coatings provide superior lubricity compared to hydrophobic coatings, such as silicone, when tested against a biological tissue countersurface.
In addition to lowering the coefficient of friction of the coated device, an effective lubricious coating must strongly adhere to the device surface. The lubricious coating should remain adhered to the device surface during potentially extended periods of storage, as well as in response to abrasive forces encountered during preparation and use. Poor adhesive strength is undesirable because the lost coating may be left behind inside the patient during use, with detrimental affects and a corresponding decrease in the lubricity of the device. Typically, a trade off exists between a coating""s lubricity and the coating""s adhesive and cohesive strength, so that attempts to increase the adhesive strength of lubricious coatings may inadvertently decrease the lubricity of the coating. Consequently, one difficulty has been providing a highly lubricious coating that strongly adheres to a device surface.
In angioplasty procedures, there may be restenosis of the artery, i.e. reformation of the arterial blockage, which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. One difficulty has been the treatment of restenosis following an angioplasty procedure. Various medical devices, such as stents or catheters, have been coated with therapeutic or diagnostic agents, to provide localized and possibly extended exposure of the tissue to the agent. For example, drugs which prevent the proliferation of smooth muscle cells, or which promote the attachment of endothelial cells, can be coated on a stent which is then implanted at the site of a stenosis within a patient""s blood vessel, to thereby inhibit restenosis following an angioplasty or stent implantation procedure. However, the agent must be strongly adhered to the device surface for effective delivery within the patient. Moreover, controlled release of the agent from the device surface within the patient may be required as part of the therapeutic or diagnostic regime.
Another therapeutic challenge is the stabilization of vulnerable plaque. The term xe2x80x9cvulnerable plaquexe2x80x9d refers to an atherosclerotic plaque which may rupture and/or erode, with subsequent thrombosis. The most common type of vulnerable plaque contains a core filled with lipid, cholesterol crystals and cholesterol esters, macrophages, and other cells, having a fibrous cap which can become weakened. When ruptured, the luminal blood becomes exposed to highly thrombogenic core material, such as tissue factor (TF), which can result in total thrombotic occlusion of the artery. There is increasing evidence that the propensity of an atherosclerotic plaque to rupture is related to activity of matrix metalloproteinases (MMPs), largely synthesized by macrophage-derived foam cells. Specifically, MMPs may degrade extracellular matrix proteins such as Types I and III collagen which are a signifcant source of fibrous cap structural integrity. Thus, chronic and/or local inflammation, typically a result of monocyte adhesion, in the plaque can lead to destabilization of these vulnerable plaques and lead to acute coronary syndromes (via thrombosis).
It would be a significant advance to provide a hydrophilic coating which strongly adheres to a surface of a medical device, or a therapeutic or diagnostic coating strongly, but potentially releasably, adhered to the surface of a medical device. The present invention satisfies these and other needs.
The invention is directed to a method of providing a coating on an intracorporeal medical device, and the coated medical device, or component thereof, produced thereby. A durable coating is provided on the medical device which modifies the device surface with a therapeutic, diagnostic, lubricious or other active agent. The coating of the invention may be used on a variety of medical devices including stents, catheters, guidewires, cardiac pacing leads, vascular grafts, and the like.
In one embodiment, the coating on the intracorporeal medical device generally includes a base coat and a top coat. The base coat has a binding component and a grafting component, and is used to strongly adhere to the surface of the device and also to strongly bond to the top coat. Specifically, the binding component binds to both the top coat and to the grafting component, and the grafting component adheres to the device surface. The base coat containing the grafting component and binding component in a suitable carrier such as a solution is first applied to the surface of the device. The base coat is preferably polymerized, e.g., exposed to polymerizing radiation to polymerize the grafting component, and the grafting component is bonded to the binding component and adhered to the surface of the device to form a base coat on the device. The device is then coated with a top coat containing a desired therapeutic, diagnostic, or hydrophilic agent. The top coat may be applied in a solution which is allowed to evaporate, to form a top coat with a therapeutic, diagnostic, or hydrophilic agent. In another embodiment, the device is coated with a top coat comprising a linking agent, and the linking agent is exposed to the therapeutic, diagnostic, or hydrophilic agent to form a complex therewith, to thereby form the therapeutic, diagnostic or hydrophilic coating of the invention. Because the top coat bonds to the base coat, the therapeutic, diagnostic, or hydrophilic coating produced will not readily wear off.
In one embodiment, the base coat comprises a binding component which is a homofunctional compound having homofunctional groups which covalently bond to functional groups in the top coat. In a preferred embodiment, the homofunctional binding component is grafted to the grafting component by a hydrogen abstraction mechanism, in which the grafting component is activated by initiators and covalently bonds to the binding component. In another embodiment, the base coat comprises a binding component which is a heterofunctional compound having a first functional group for covalently bonding with the grafting component, and a second functional group for covalently bonding to functional groups in the top coat.
As mentioned above, the binding component of the base coat bonds to the top coat. In one embodiment, the therapeutic, diagnostic, hydrophilic or other active agent has functional groups which directly bond to functional groups of the binding component. In another embodiment, the therapeutic, diagnostic, or hydrophilic agent is bound to the binding component by a linking agent in the top coat. The linking agent may inherently have functional groups, or may be modified to include functional groups, which bond to functional groups of the binding component. The linking agent may be bound to the base coat and thereafter exposed to the therapeutic, diagnostic or hydrophilic agent, or alternatively, the linking agent may be exposed to the agent before or during the binding of the linking agent to the base coat.
A variety of suitable linking agents may be used, including avidin-biotin complexes, and functionalized liposomes and microsponges and microspheres. Avidin is a polypeptide composed of at least 128 amino acid residues. Typically however, the single polypeptide chain is a subunit associated with three essentially identical polypeptide chains, forming a tetramer. Avidin as a receptor is typically used in conjunction with its highly specific ligand, biotin, C10H16N2O3S. An avidin tetramer will bind 4 biotin molecules in solution in a noncovalent interaction which has a binding constant of about 1015 Mxe2x88x921, a half-life in vivo of about 89 days, and which is essentially undisturbed by organic solvents. Biotinylation, or the process of covalently binding biotin to another molecule, typically takes place by N-hydroxysuccinimide binding. Spacer molecules may be inserted between the avidin and the base coat, or between the biotin and the therapeutic or diagnostic agent, as is known in the art, to facilitate avidin-biotin binding or improve the activity of the therapeutic or diagnostic agent. The avidin or the biotin molecule may be chemically altered to decrease the binding constant, to thereby tailor the dissociation rate in vivo, and provide controlled release of the therapeutic or diagnostic agent bound thereto. Avidin and biotin are available from a variety of commercial suppliers, such as Sigma. In one embodiment, avidin covalently binds to the binding component of the base coat, and binds to a biotinylated therapeutic or diagnostic agent, such as a biotinylated protein, antibody, peptide or oligonucleotide. However, the avidin-biotin linking agent may alternatively have biotin moieties covalently bound to the binding component of the base coat, and avidin moieties bound to the therapeutic or diagnostic agent. Alternatively, biotin may be covalently bound to the base coat and to the therapeutic or diagnostic agent, with avidin, by virtue of its multivalency with biotin, binding the two biotin moieties together.
Liposomes are lipid molecules formed into a typically spherically shaped arrangement defining aqueous and membranal inner compartments. Liposomes can be used to encapsulate compounds such as therapeutic and diagnostic agents within the inner compartments, and deliver such agents to desired sites within a patient. The agents contained by the liposome may be released by the liposome and incorporated into the patient""s cells, as for example, by virtue of the similarity of the liposome to the lipid bilayer that makes up the cell membrane. A variety of suitable liposomes may be used, including those available from NeXstar Pharmaceuticals or Liposome, Inc, if functionalized as by the procedures described herein.
Microsponges are high surface area polymeric spheres having a network of cavities which may contain compounds such as therapeutic or diagnostic agents. The microsponges are typically synthesized by aqueous suspension polymerization using vinyl and acrylic monomers. The monomers may be mono or difunctional, so that the polymerized spheres may be cross-linked, thus providing shape stability. Process conditions and monomer selection can be varied to tailor properties such as pore volume and solvent swellability, and the microsponges may be synthesized in a controlled range of mean diameters, including small diameters of about 2 micrometers or less. A standard bead composition would be a copolymer of styrene and di-vinyl benzene (DVB). The agents contained by the polymeric microsponges may be gradually released therefrom within the patient due to mechanical or thermal stress or sonication. A variety of suitable microsponges may be used, including those available from Advanced Polymer Systems, if functionalized as by the procedures described herein.
A variety of suitable therapeutic, diagnostic or hydrophilic agents may be used. For example, the therapeutic or diagnostic agent may be selected from the group consisting of proteins; peptides; oligonucleotides; antisense oligonucleotides; cellular adhesion promoting proteins or peptides including extracellular matrix proteins; polysaccharides such as heparin, hirudin, hyaluronan, and chondrotin; nitric oxide donating compounds; growth factor such as VEGF; Taxol; Paclitaxel; Carboplatin; and Cisplaten.
The therapeutic or diagnostic agents may be used for a variety of purposes, including improving the biocompatibility of the intracorporeal medical device and inhibiting restenosis. For example, antisense oligonucleotides may be used to improve biocompatibility of the medical device, or to inhibit or prevent restenosis, where the antisense oligonucleotide inhibits cell migration, inhibits synthesis of extracellular matrix proteins or growth factors, or induces apoptosis. Suitable antisense oligonucleotides are include those described in U.S. Pat. Nos. 5,470,307, 5,593,974, and 5,756,476, and Uhlmann, E. et al, Antisense Oligonucleotides: A New Therapeutic Principle, Chemical Reviews, 90(4), 544-579 (1990), incorporated by reference in their entireties. The antisense oligonucleotides may be modified with avidin or biotin, or to contain hydrophobic groups such as cholesterol, to facilitate cellular uptake and prevent degradation by nucleases. Similarly, extracellular matrix proteins may be used to improve biocompatibility of the medical device, or inhibit or prevent restenosis. Extracellular matrix proteins, such as fibronectin, laminin, collagen, and vitronectin, or synthetic peptide analogues of extracellular matrix proteins, have an amino acid sequence which contributes to cell adhesion. Synthetic peptide analogues of extracellular matrix proteins can also be used which retain the biological function but have a lower molecular weight and different solution properties. The extracellular matrix proteins or peptides will attract migrating cells within the patient, and thus inhibit restenosis by preventing the cells from accumulating in the arterial lumen. Additionally, by attracting migrating cells, they facilitate integration with tissue of implanted devices, such as stents, and wound healing, and the uptake by cells of other therapeutic agents bound to the device surface. Additionally, the extracellular matrix proteins bound to the device surface may facilitate in vitro seeding of endothelial cells to the device prior to implantation or introduction of the device within the patient. In one embodiment, the extracellular matrix protein vitronectin is bound to the device surface, and an antibody to the B1 integrin subunit is bound to the device surface or is delivered locally or systemically. This antibody has been shown to block cellular adhesion to all extracellular matrix proteins except vitronectin, thereby enhancing the adhesive power of the modified device surface. Similarly, nitric oxide donor drugs may be used to improve biocompatibility of a medical device, and may also prevent or inhibit platelet aggregation and promote wound healing. Additionally, nitric oxide donor drugs may be used as a vasodilator relaxing smooth muscles of a vessel prior to, during, and/or after angioplasty or stent placement. A variety of suitable nitric oxide donor drugs can be used including nitric oxide-polyamine complexes, 2-methyl-2-nitrosopropane, S-Nitroso-N-acetyl-D,L-penicillamine, 3-morpholoinosydoimine, sodium nitrate, s-nitrosoglutathione, sodium nitroprusside, and nitroglycerine. The structure and mechanisms of suitable nitric oxide donor drugs are disclosed in U.S. Pat. No. 5,650,447, incorporated by reference in its entirety.
In one embodiment, the therapeutic agent is superoxide dismutase or a superoxide dismutase mimic (i.e., mimetic). Superoxide dismutase is an endogenous enzyme which catalytically converts superoxide to hydrogen peroxide and oxygen. Superoxide is a highly oxidative species present in disease states, which reacts with endogenous nitric oxide (NO) to produce the oxidative species peroxynitrite, a cell damaging oxidative species which also causes lipid peroxidation. Moreover, superoxide consequently lowers the endogenous NO concentration. Endogenous NO has a number of beneficial effects, and one aspect of the invention is a method of preventing or inhibiting the removal of endogenous NO by superoxide, to, for example, prevent or inhibit restenosis, and to stabilize a vulnerable plaque from erosion and/or rupture and thrombosis. In a presently preferred embodiment of the invention, the superoxide or a superoxide mimic has a pendant functional ligand which covalently bonds to a compatible reactive group of a coating component on a surface of a medical device. The terminology xe2x80x9csuperoxide mimicxe2x80x9d should be understood to refer to compound which mimics the action of superoxide by, for example, catalytically dismutating superoxide.
In one embodiment, superoxide dismutase or a superoxide dismutase mimic is presented on a surface of the medical device to prevent or inhibit restenosis, at least in part by preserving endogenous NO. Benefits of endogenous NO which are believed to prevent or inhibit restenosis include vasorelaxation, inhibition of smooth muscle cell migration and extra-cellular matrix synthesis, and inhibition of platelet and inflammatory cell aggregation and adhesion. In another embodiment, superoxide dismutase or a superoxide dismutase mimic is presented on a surface of the medical device to prevent or inhibit rupture and/or erosion of vulnerable plaque, at least in part by preserving endogenous NO. NO has been shown to reduce monocyte adhesion. Thus, by reducing monocyte adhesion, fewer macrophage-derived foam cells and fewer MMPs would be present, resulting in stabilization of the plaque. In one embodiment, the vulnerable plaque is stabilized with a stent or catheter device having a superoxide dismutase or a superoxide dismutase mimic coating of the invention to inhibit or prevent inflammation and resulting thrombosis processes.
A variety of suitable hydrophilic or lubricious compounds can be used as the hydrophilic agent. The hydrophilic agent typically has functional groups which directly bond to the binding component of the base coat. Because the hydrophilic compound is bound to the base coat, it will not readily wear off even after repeated hydration and abrasion. To hydrate the hydrophilic coating on the device and render the coating highly lubricious, the coated device may be exposed to aqueous fluid either before insertion into a patient or by contact with body fluid while inside the patient.
In another embodiment, a base coat is not used, and a coating is provided on the intracorporeal medical device, which in a presently preferred embodiment is a hydrophilic coating generally including a hydrophilic polymer, an ionic compound with at least one inorganic ion, and a grafting component. The grafting component is polymerized as outlined above, so that the grafting component grafts to the device and crosslinks to the hydrophilic polymer, to form a hydrophilic coating on the device. When the coated device is hydrated, the coating absorbs water and is highly lubricious, but does not dissolve in the aqueous or blood medium because the hydrophilic polymer is immobilized by the grafted network. Moreover, the ionic compound, or salt, increases the lubricity of the hydrophilic coating by providing uncrosslinked domains in the crosslinked matrix. Because the ability of a hydrophilic polymer to absorb water is decreased when the polymer is crosslinked, the salt enhances the polymer lubricity by disrupting the crosslinking of the hydrophilic polymer into the grafting component crosslinked network. Therefore, when the hydrophilic coating is hydrated by exposure to a solvent and the salt dissolves, these uncrosslinked domains provide additional lubricity by increasing the contact between the hydrophilic polymer and the countersurface, e.g. the patient""s vessel wall, and hence additional lubricity. Additionally, the salt affects morphology of the hydrophilic compound, resulting in improved resistance to particle shedding from the coated device.
The coating of the invention can be applied to any device having a polymeric surface, as for example, a catheter formed of conventional materials, or a metal device, such as a metal guidewire or stent, having a polymer primer coat. For example, the catheter components may be formed of high density polyethylene, polyethylene terephthalate, and polyolephinic ionomers such as Surlyn(copyright), nylon and the like which are frequently used to form dilatation balloons or catheter shafts. Additionally, the therapeutic, diagnostic, or hydrophilic coating of the invention can be applied directly to a metal device. For example, in the embodiment of the invention having a base coat and a top coat, the base coat adheres, as by Van der Waals forces, to the metal surface of the device, so that a polymeric primer coat need not be used.
In the embodiment of the coating of the invention having a hydrophilic agent, the coated device has a superior hydrophilic coating which is highly lubricious against biological tissue and is strongly bound to the device surface due to the grafting component used alone or in combination with the binding component. In the case of a PTCA catheter or guidewire, the coating serves to enhance device access to distal lesions and the ease with which a device crosses small diameter athlerosclerotic lesions.
In the embodiment of the coating of the invention having a therapeutic or diagnostic agent bound to the medical device surface, directly or via a linking agent, the coating of the invention provides localized delivery of the therapeutic or diagnostic agent. Similarly, the coating of the invention improves the residence time of the therapeutic or diagnostic agent. By binding the agent to the device, the rapid clearance from the bloodstream of the therapeutic agent, as for example when the body""s immune system phagocytizes the therapeutic agent or a liposome containing the agent, is avoided.